1. Field of the Invention
The present invention relates to a decay heat removal system comprising a heat pipe heat exchanger, and, more particularly, to a decay heat removal system comprising a heat pipe heat exchanger, by which decay heat in a liquid metal-cooled reactor is passively removed.
2. Description of the Related Art
A liquid metal-cooled reactor is a nuclear reactor, in which energy produced by a nuclear fission reaction using fast neutrons is absorbed into a liquid metal coolant and thus transferred to a steam generator to generate steam, and then an electric generator is operated using the generated steam to produce electricity.
Recently, in order to prepare for a steam generator losing its function of normally removing decay heat (residual heat) generated from a core of a nuclear reactor after the reactor has been scrammed, a liquid metal-cooled reactor is equipped with a passive decay heat removal system for removing the decay heat remaining in its core using natural phenomena.
FIG. 1 is a schematic view showing a conventional decay heat removal system for a liquid metal-cooled reactor.
Referring to FIG. 1, a conventional decay heat removal system 10 for a liquid metal-cooled reactor, in which pools are directly cooled, includes a decay heat exchanger 11, a sodium-air heat exchanger 12, and a sodium loop 13 for heat removal.
The decay heat exchanger 11 is provided in a hot pool 15 such that it is located under the liquid level of hot sodium, the sodium-air heat exchanger 12 is provided at the upper portion of a building (not shown) provided with the liquid metal-cooled reactor, and the sodium loop 13 for heat removal serves to connect the decay heat exchanger 11 with the sodium-air heat exchanger 12.
According to the above-configured decay heat removal system 10, decay heat generated from the liquid metal-cooled reactor is discharged to the atmosphere, which is a final heat sink, by the natural circulation of sodium using the difference in density of sodium in the sodium loop 13, caused by the difference in height between the decay heat exchanger 11 into which the decay heat is introduced and the sodium-air heat exchanger 12 from which the decay heat is removed to the atmosphere.
In the above-configured decay heat removal system 10, dampers 18 are respectively provided in an air inlet 16 and an air outlet 17 of the sodium-air heat exchanger 12 to control the amount of air, and valves 19 are provided in the sodium loop 13 to control the amount of sodium, thereby preventing the solidification of sodium in the sodium loop 13 and controlling the amount of heat loss during normal operation.
However, the decay heat removal system 10 is problematic in that, although its heat removal function is performed by just the natural circulation of a heat transfer medium (sodium), the dampers 18 and valves 19 are intentionally operated, and thus a fully passive decay heat removal system cannot be realized, thereby deteriorating the operational safety related to the operational reliability of the decay heat removal system 10.
FIG. 2 is a schematic view showing another conventional decay heat removal system 20 for a liquid metal-cooled reactor.
Referring to FIG. 2, as another conventional decay heat removal system 20 for a liquid metal reactor, a fully passive decay heat removal system, including a decay heat exchanger 24, a sodium-air heat exchanger 26 whose air inlet 27 and air outlet 28 are not provided therein with dampers and a sodium loop 25 for heat removal which is not provided therein with valves, is employed.
In the decay heat removal system 20, the decay heat exchanger 24 is provided over a cold pool 23 in a vertical-type cylindrical tube 21 provided to connect the cold pool 23 with a hot pool 22.
The difference in liquid levels between the hot pool 22 and the cold pool 23 is maintained constant during normal operation by the pumping of a primary pump (not shown).
For this reason, when decay heat is generated during normal operation, the decay heat in the hot pool 22 is absorbed into the decay heat exchanger 24 by radiation.
The decay heat exchanger 24 is connected to the sodium-air heat exchanger 26 provided at the upper portion of a reactor building (not shown) in which the liquid metal-cooled reactor is installed. The decay heat absorbed into the decay heat exchanger 24 by radiation is transferred to the sodium-air heat exchanger 26 through the sodium loop 25 by the difference in density of sodium, caused by the difference in height between the decay heat exchanger 24 and the sodium-air heat exchanger 26, then to the outside.
Meanwhile, when the reactor core is scrammed, the operation of primary pump is also stopped, so that the difference in liquid level between the hot pool 22 and the cold pool 23 disappears and simultaneously sodium in the hot pool 22 directly comes into contact with the decay heat exchanger 24, with the result that the decay heat exchanger 24 can absorb heat from the sodium in the hot pool 22 by convection.
Therefore, the decay heat exchanger 24 having absorbed the heat from the sodium in the hot pool 22 by convection transfers the absorbed heat to the sodium-air heat exchanger 26 through the sodium loop 25, thereby discharging the heat to the outside.
That is, in the conventional decay heat removal system 20, decay heat is discharged to the outside through a heat transfer process by radiation when the liquid metal-cooled reactor (not shown) is normally operated, whereas the decay heat is discharged to the outside through a heat transfer process by convection when the operation of the primary pump is stopped.
Accordingly, this conventional decay heat removal system 20 is advantageous in that a fully passive decay heat removal system is realized by removing artificial means such as dampers, valves and the like, but is problematic in that, when the temperature of air or a sodium loop decreases, liquid sodium in the sodium loop solidifies, thus deteriorating its heat removal function which is important for reactor safety.